There is substantial interest in being able to type human leukocyte antigens (HLAs) for a variety of reasons. In many situations it has been found that specific HLA alleles may be associated with a susceptibility to a particular disease. For example, HLA-B27 has been associated with ankylosing spondylitis and related diseases. When transplanting organs to a host it is desirable that the organs be matched, so as to minimize the risk of rejection. HLA typing may also find application is determining lineage, epidemiology and the like.
There is an extensive family of HLA antigens divided into Class I and Class II. In each of the classes, them are polymorphic regions. These polymorphisms may or may not provide for epitopes which will induce an immune response, which will allow for the preparation of antisera or monoclonal antibodies which are specific for a specific HLA allele and able to distinguish that HLA allele from other HLA alleles.
This situation is exemplified by the cross-reactivity between HLA-B27 and HLA-B7 where monoclonal antibodies are not readily available which are specific for HLA-B27, and which do not cross-react with HLA-B7 or any other HLA alleles.
Since mammals are diploid, there will be always be two alleles present at every HLA locus. Thus, unless one can determine specifically a particular HLA allele, one cannot be certain whether there are two different alleles or one is observing cross-reactivity. There is, therefore, substantial interest in developing methods which will allow for the accurate detection of a particular HLA allele in those cases where substantial cross-reactivity is observed with other HLA alleles.